Steam is a convenient form in which to transport, distribute, and supply energy, because it has a high heat content, it is fluid and thus can be divided or merged, and it may be used for its heating effect or for motive power. Steam may be used for direct heating applications such as in a thermocompressor, where high-pressure steam may be used to boost low-pressure steam to a higher pressure at which it can be used. For instance, an industrial plant may have an excess of low-pressure steam at 5 to 15 lb./in.sup.2 and need 50 to 100 lb./in.sup.2 steam for dryers, reboilers, or some other use where higher temperature is needed. A thermocompressor can boost the low-pressure steam to the 50 to 100 lb./in.sup.2 range by using live steam directly from the boiler on the jet of the thermocompressor. When used for heating effect, however, steam is most often used for indirect applications, in which a heat transfer surface is disposed between the steam and material to be heated, such as condensors, stage heaters, process heat exchangers, reboilers, evaporators, space heaters and the like. The most common surface heat exchanger, the sheet-and-tube type, transfers heat from steam or another hot fluid to a colder fluid principally by conduction across a metal tube wall separating the two. Shell-and-tube heat exchangers can be of several designs. The more complex designs are usually more efficient, but may be more costly and more difficult to clean and maintain.
In industrial plants, large quantities of high-pressure steam are often required for a wide variety of purposes. Steam is generally generated in boilers at pressure of about 175 to 600 lb./in.sup.2, and in power stations up to about 2400 lb./in.sup.2, which is much higher than, for instance, the excess pressure of about 7 lb./in.sup.2 in relation to the external air commonly used in low-pressure, residential steam-heating systems.
Steam employed in steam-using devices eventually condenses, and the condensate is drained or otherwise removed from the area of steam use, for instance from the heat exchange surfaces, and is collected. This is the job of the trap and subsequent condensate collection and forwarding systems. Traps vent air or other noncondensible gases, drain the condensate with a minimum of restriction, and promptly sense the presence of steam and restrict its loss from the system.
The utility industry, which is the largest energy consumer in most industrialized countries, use steam for motive power, as do many moderate-sized industrial plants that may put steam through a turbine at high pressure and then use the exhaust steam for process needs. Turbines are the major prime movers, although reciprocating piston steam engines are still found in use. In steam turbine operations the exhaust steam may be discharged to a condensor at subatmospheric pressure or into process steam headers under pressure (e.g., 100 lb./in.sup.2 is common in the paper industry).
The flow of steam through a system, particularly an industrial installation, to the eventual collection of condensate, may be complex, and the steam moving through a system may be generated in a plurality of steam-generating devices, such as boilers, and steam from different boilers may take, at least in part, different routes through a system. As it passes through a system, the steam is in contact with many areas thereof, and thus its condensate may provide a great wealth of information concerning operational variations within the system. For instance, a very serious problem with process equipment is corrosion, the principal agents of which are oxygen and carbon dioxide. The impurities in the steam's condensate can disclose the existence of a corrosion problem. For instance, a drop in condensate pH may indicate an undesirable concentration of carbon dioxide in the system. Evaluation of steam condensate is an important diagnostic tool. When multiple steam-generating sources are used, however, the ability to identify the steam source would greatly improve the diagnostic method. For instance, if corrosion problems develop in fewer than all of the steam-generating sources, the ability to quantify the proportion of condensate from a given source or group of sources would be highly advantageous, particularly if there are multiple steam routes, and multiple condensate collectors. It would permit one to determine from which steam-generating sources the condensate impurity(ies) of concern were derived. A determination of the proportion of condensate from one of a plurality of steam-generating sources would also permit one to determine in turn a more accurate picture of the extent of the problem, for one would know the extent of dilution of such impurity-containing condensate with other condensate. Thus it would be highly advantageous to be able to identify steam from its generation to the collection of its condensate. It would be highly advantageous to so identify steam quantitatively. It would be highly advantageous to identify steam by a continuous monitoring system, for the purpose of determining the source of impurities and for other reasons. For instance, in a system designed so that a given condensate should contain a given proportion of condensate generated by a certain source or passing in a given amount a certain point in the system, the ability to quantitatively identify steam could be employed as a warning signal, that the amount of steam from a source or passing a point in the system has fallen off, or has risen.
In short, the ability to quantitatively identify steam moving from a given point (the steam source or other point) to a sampling point, and distinguish the condensate from that steam, or the proportion thereof, from the condensate of other steam, would greatly enhance the ability to diagnose both chemical and equipment problems in a steam-using system.
It is an object of the present invention to provide a means and method for so identifying steam, which means and method are adaptable to highly advantageous continuous monitoring systems. These and other objects of the present invention are described in more detail below.